The invention concerns a mixing device comprising a container for accommodating material to be mixed, a mixing tool arranged in the interior of the container and a heating device for heating the material to be mixed.
Mixing, that is to say combining at least two starting materials having different properties to provide a mixture of substances, is a fundamental operation in mechanical industrial process engineering.
The aim when using a mixing device is to achieve the highest possible level of homogeneity of the new substance. To achieve the desired homogeneity for example mixing devices having a rotating mixing container are used.
In such devices at least one mixing tool is arranged generally eccentrically in the interior of the container. When the container rotates the material to be mixed which is accommodated in the container is transported towards the mixing tool and thoroughly mixed by means thereof. With such mixers, materials of any kind and consistency can be processed quickly and with a high quality.
Experience has shown that a mixer having a rotating container mixes without noticeable separation of the constituents of the mixture as complete rotational turn-over of the material is achieved during a revolution of the mixing container.
As many mixing processes are linked to a chemical reaction which presupposes the supply of a given activation energy, it is already usual for many situations of use for the material to be mixed to be heated during mixing. That is also necessary if thermal liquid removal is to take place in superposed relationship during the mixing operation.
Therefore to permit heating of the material to be mixed in the mixer some mixing devices have a heating casing which surrounds the container wall and is in contact therewith. Heat energy can then be fed into the mixing container by way of the heating casing. Depending on the respective heat transfer medium the heating casing is either in the form of a double casing for hot water or thermal oil heating or, when higher design pressures are involved for vapour heating, the heating casing is in the form of a casing with projections thereon or with half-tubes welded thereto. The known solutions are limited in respect of their maximum wall temperature due to the maximum permissible temperature of the heat transfer medium or in the case of vapour heating due to the necessary compression strength of the double casing.
In addition it is not possible with those solutions to implement fast heating curves up to very high wall temperatures as the heating rate is limited by the heat transfer coefficient from the liquid or the vapour phase to the container wall and the pressure losses and thus the flow speed of the heat transfer medium in the heating casing.